Closure cap liners having oxygen barrier properties

ABSTRACT

Liners with improved oxygen barrier properties for use with closure caps are disclosed. The liners are made of a composition that includes a thermoplastic elastomer, polyisobutylene and polybutylene. The liner is adhered to the inner facing surface of a closure cap.

[0001] The present invention generally relates to improved oxygenbarrier liner compositions for plastic closures and more particularly,to homogeneous thermoplastic elastomer liner compositions which providean effective barrier to oxygen ingress into the containers and which areadvantageously characterized by improved physical properties such asincreased tensile strength and elongation. This invention also relatesto a method for making such liners from such plastic compositions and toclosures for containers for food and beverage products which closuresinclude these liner compositions.

BACKGROUND OF THE INVENTION

[0002] Closures for use in food and beverage containers include aclosure shell formed of metal, plastic or both metal and plastic and aretypically provided with a liner on the inner surface of the closureshell end panel. The liner is intended to provide a hermetic sealbetween the closure member and the container opening.

[0003] Notwithstanding the lined closure, oxygen can permeate theclosure shell or enter through spaces between the closure shell and thecontainer. Oxygen can adversely affect beverage and food products storedwithin a container since a small amount of oxygen can alter the taste ofthe beverage or food product or cause spoilage of the product.Accordingly, it is desirable that the liners be made of or include amaterial that is a barrier to oxygen. Efforts to provide a liner that isan effective barrier against oxidation of the food or beverage storedwithin a container are described in the prior art.

[0004] U.S. Pat. No. 5,955,163 to White discloses a gasket for closuresused with beverage containers. The gasket is formed of a thermoplasticmaterial which includes, for example, a hydrogenated copolymer ofstyrene and conjugated diene or functionalized derivative thereof and arubbery polymer such as butyl rubber which, according to this patent,further prevents ingress of oxygen and volatile odors. The gasket isused with metal crown caps.

[0005] U.S. Pat. No. 4,684,554 to Ou-Yang describes a multi-layered sealthat includes a pulpboard backing, a wax coating over the pulpboard,aluminum foil and a heat-sealable polymeric coating over the foil. Thealuminum foil acts as an oxygen barrier. The multi-layered seal ismounted inside the closure of a container. The container and the closure(with the seal) is treated in a radio frequency field, such that whenthe closure is removed from the container, the pulpboard backing twistsfree from the foil which remains bonded to the lip of the container. Thefoil is then peeled off the lip of the container when access to thecontents is desired. While aluminum foil provides a good barrier tooxygen, from the standpoint of a consumer, such peelable seals are lessthan desirable because of the difficulty often encountered in removingthem from the opening of the container.

[0006] Another example of a closure with an oxygen absorbing liner isdescribed in U.S. Pat. No. 5,381,914 to Koyama et al. The linerdescribed therein is made of a resin which is blended with an oxygenabsorbing agent. The composition can be applied to the entire innersurface of the closure shell or, more typically, may be incorporated asa layer of a laminated structure. The laminate includes the layer of theoxygen absorbing agent and a layer of resin interposed between theoxygen absorbing layer and the closure shell. The oxygen absorbing layercan be made of a thermoplastic elastomer with the oxygen absorbing agentblended therein. Examples of suitable organic oxygen absorbing agentsinclude phenol-type resins, ascorbic acids, saccharides and the like.

[0007] U.S. Pat. No. 5,143,763 to Yamada et al. describes amulti-layered seal for use with bottle closures that include a layer ofan oxygen absorbent composition and an oxygen permeable film coveringthe oxygen absorbent composition. The composition includes an asymmetricporous membrane where the outer surface is formed as a dense skin layer.The dense skin layer protects the oxygen absorbent layer from beingcontacted by the food or beverage stored within the container.

[0008] While the liners or seals described above may be effective inlimiting the amount of oxygen ingress into the container, furtherimprovements in the field of oxygen barrier liners for closures aredesirable.

[0009] For example, it would be desirable to provide a liner which actsas an oxygen barrier and can be used in association with resealableplastic closures. It would also be desirable that such liners notrequire peeling or removal by the consumer.

[0010] In addition to providing a barrier to oxygen, liners for use infood or beverage container closures should possess other properties. Forexample, the liner and the plastic compositions used for such linersmust possess good to excellent adhesion to the inner surface of theclosure preferably without the use of a separate adhesive.

[0011] Also, the sealing provided by the liner should not be such thatit is difficult for the average user to open the container. Accordingly,the liner must have good “torque removal” properties to allow for easyremoval (e.g., by unscrewing) of the cap without having to use excessforce.

[0012] The liner should also be made of a composition that is easy toprocess. Oil-based plasticizers, such as mineral oil, have been includedin liner compositions to improve the processability of the composition.However, under certain conditions, extractable compounds from themineral oil have been known to migrate from the liner composition to thestored food product. Plasticizers such as mineral oil have also beenknown to exhibit an odor and/or affect the taste of the food product.Thus, it would be desirable to provide a liner that is easy to processbut (1) does not include an oil or other plasticizer, (2) does notaffect the taste of the stored food product, and (3) is substantiallyodorless.

[0013] It would also be desirable to provide a liner that can be easilyformed into flat liners by known techniques such as injection moldingand cold punch molding, and that can otherwise be easily incorporatedinto the closure.

[0014] The plastic composition of the present invention and liners madefrom such plastic compositions address at least all of theabove-described objectives. For example, our studies have shown that thepreferred single layer liner in accordance with the present inventionhas an oxygen ingress rate of between approximately 4-8 cc/m²/day, a100% modulus greater than approximately 260 psi, % elongation of greaterthan approximately 350 and a tensile strength (psi) greater thanapproximately 500. Also, we have observed that the desirable propertiesdescribed above can be affected by the relative proportions of thecompounds used in the liner composition. For example, excesspolybutylene will negatively affect the sealability of the liners inrelation to the container opening, whereas too little polybutylene canreduce the adhesion of the liner to the inner surface of the closurecap. An amount of polyisobutylene that is significantly lower than theamount used in the composition of the present invention will reduce theoxygen barrier properties, while too much polyisobutylene can make thecomposition more difficult to process.

SUMMARY OF THE INVENTION

[0015] There are several different aspects to the present invention. Inone aspect, the present invention is directed to a closure cap liner orgasket composition comprising a blend of a thermoplastic elastomer,polybutylene and polyisobutylene. In another aspect of the presentinvention, the plastic composition can also advantageously include amicrocrystalline wax.

[0016] Plastic compositions of the type described above exhibitexcellent oxygen barrier properties and, therefore, are useful inclosures for food or beverage containers. Accordingly, in anotheraspect, the present invention is directed to a container closurecomprising a plastic shell having an end panel and an integral skirtthat extends downwardly from the periphery of the skirt. The end panelhas an inner-facing surface and includes a substantially oxygenimpermeant liner which is adhered to at least a portion of theinner-facing surface. The liner is made from a material including athermoplastic elastomer, polybutylene and polyisobutylene. In anotheraspect of the present invention, the liner can also advantageouslycontain a microcrystalline wax.

[0017] The present invention is also directed to a method for providinga liner for a container closure. The method includes (1) combining andmixing polyisobutylene with a thermoplastic elastomer, (2) addingpolybutylene to the mixture of polyisobutylene and thermoplasticelastomer to provide a blend, and (3) forming the blend into a liner. Amicrocrystalline wax can be advantageously added to the blend ofthermoplastic elastomer, polybutylene and polyisobutylene. The liner canbe formed into a disc or a ring adhered to the inner-facing surface ofthe closure.

[0018] The objects of this invention are achieved with closure caps thatinclude liners made from a composition that comprises a thermoplasticelastomer, polyisobutylene and polybutylene.

DETAILED DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a side view of a plastic closure of the type used inconnection with the present invention;

[0020]FIG. 2 is a cross-sectional view of a container closure with aliner embodying the present invention adhered to the inner surface ofthe closure;

[0021]FIG. 3 is a plan view of the inner surface of a closure with theliner of FIG. 2 adhered to the inner-facing surface of the closure;

[0022]FIG. 4 is a plan view of a closure with another embodiment of theliner adhered to the inner-facing surface of the closure; and

[0023]FIG. 5 is a cross-sectional view of the closure of FIG. 1 with theliner of FIG. 4 adhered to the inner surface of the closure end panel.

DETAILED DESCRIPTION OF THE INVENTION

[0024] The plastic composition of the present invention will bedescribed below in the context of its preferred use, namely, as a linerfor a plastic closure of a food or beverage container. It will beappreciated, however, that the plastic composition of the presentinvention is not limited to such use. The plastic composition of thepresent invention can be used in any other application where, forexample, a material with oxygen barrier properties is desired, and/orwhere a material exhibiting excellent adhesion to a plastic substrate isdesired.

[0025] Turning now to the drawings, FIG. 1 shows a container 10 with aclosure 12 secured over the open mouth of the container. Closure 12includes a shell generally designated by the reference numeral 14. Shell14 includes an end panel 16 and a skirt 18. In the illustratedembodiment closure 12 further includes a tamper-evident band 20integrally formed with and secured to the base of the skirt by aplurality of frangible bridges 21. Closure 12 can typically be made by,for example, injection molding from a thermoplastic composition such as,for example, a polyolefin such as polypropylene. Closure 12 can be madeof polyethylene or a blend of polyethylene and polypropylene.Alternatively, closure 12 can be made of a plastic/metal compositematerial or entirely of metal.

[0026] As best shown in FIG. 2, shell 14 seals the open mouth ofcontainer 10 defined by end finish 24. As further shown in FIGS. 2 and3, closure shell 14 includes a liner 28 adhered to the inner-facingsurface of shell 14. Liner 28 can be in the shape of a circular discthat covers substantially the entire inner-facing surface of end panelof shell 14 (FIG. 3). Alternatively, liner 14 can be in the shape of aring which covers only the annular periphery of the inner-facing surfaceof the shell (FIG. 4). In any event, liner 28 should contact the endfinish of the container walls to provide a hermetic seal between closureshell 14 and the opening and, thereby, limit oxygen ingress from theoutside environment into the container interior.

[0027] Liners of the type shown in FIGS. 1-5 can be made of acomposition comprising a thermoplastic elastomer, polyisobutylene andpolybutylene and other additives that, among other things, provides aneffective barrier to oxygen, has good torque removal properties, andprovides good adhesion to the inner surface of the plastic closure shell14. The compositions are easy to process by known processing andcompounding methods, and moldable into a liner of the type describedabove.

[0028] In one particular embodiment, the plastic composition includes athermoplastic elastomer, a compound for improving the oxygen barrierproperties of the composition and one or more compounds to improveadhesion, torque removal and/or processability. The thermoplasticelastomer selected is preferably substantially odorless and tasteless.

[0029] Thermoplastic elastomers are polymers or blends of polymers thatcan be processed and recycled in the same way as a conventionalthermoplastic material, but that also have a rubber-like quality andperformance similar to that of rubber. Thermoplastic elastomers can beobtained by combining a thermoplastic polyolefin with an elastomericcomposition in a way such that the elastomer is intimately and uniformlydispersed as a particle phase within a continuous phase of thethermoplastic polyolefin.

[0030] Examples of thermoplastic elastomers which can be included in theplastic composition of the present invention are, for example, athermoplastic polyolefin homopolymer or co-polymer blended with anolefinic rubber which is fully cross-linked, partially cross-linked ornot cross-linked at all. In a preferred embodiment, the thermoplasticelastomer composition can be a resinous polymer of propylene and abutyl-based cross-linked rubber of the type described in U.S. Pat. No.5,843,577 to Ouhadi et al., incorporated by reference herein. As furtherdescribed in U.S. Pat. No. 5,843,577, the thermoplastic elastomer caninclude other additives, including lubricants such as polyamides andother additives such as, but not limited to, anti-blocking agents.Lubricants are typically added to soften a material and aid in theprocessing of certain tacky materials. Lubricants can also improve thetorque removal properties of a liner made from the composition.

[0031] Other examples of suitable thermoplastic elastomers are thethermoplastic elastomers sold by Advanced Elastomer Systems under theproduct name Trefsin®. In U.S. Pat. No. 6,062,269, Trefsin® is generallydescribed as a thermoplastic resin of the alloyed material of apolypropylene and an isobutylene-isoprene rubber.

[0032] In another example, the thermoplastic elastomer composition caninclude an ethylene-propylene copolymer and rubber which can becross-linked and/or can include a terpolymer of ethylene, propylene anda diene. Examples of such thermoplastic elastomers include thecommercially available Santoprene®. Santoprene® is believed to includean ethylene, propylene and diene terpolymer. Santoprene® and otherthermoplastic elastomers like it are available from Advanced ElastomerSystems, L.P. of Akron, Ohio.

[0033] The thermoplastic elastomer used in the composition of thepresent invention can also be a blend of one or more thermoplasticelastomers.

[0034] Also useful are thermoplastic elastomeric block 1.5 copolymers ofthe saturated A-B-A type based on styrene and butadiene units. Forexample, styrene-ethylene butylene-styrene (SEBS) type block copolymerscan be used. Such co-polymers are sold under the trade name Kraton-G®(e.g., Kraton-G 1652 and Kraton-G 2705) and are available from the ShellChemical Company.

[0035] Although some of the thermoplastic elastomers described abovemay, to some degree, provide a barrier to oxygen, to further enhancesuch oxygen barrier properties, other compounds can be added to theplastic composition. For example, butyl rubbers such as polyisobutyleneare desirable because they provide good oxygen barrier properties.Accordingly, the thermoplastic elastomer can be combined with aneffective amount of polyisobutylene. Polyisobutylene is available from avariety of suppliers including the Exxon Corporation.

[0036] The thermoplastic elastomers described above can be combined withother additives to improve adhesion of the liner to the closure shell.Where the shell is made of a thermoplastic polyolefin such aspolypropylene, improved adhesion is provided by adding an effectiveamount of other polyolefin. One such polyolefin is polybutylene, whichprovides improved adhesion of the plastic composition to thepolypropylene shell of a closure. Polybutylene also improves the flowcharacteristics and overall processability of the plastic composition.An example of a polybutylene that is suitable for inclusion in theplastic composition of the present invention is PB 0400 available fromMontell Corporation. Alternatively, or in addition to polybutylene,polypropylene may be added to the thermoplastic elastomer of thecomposition.

[0037] As discussed above, closures for food and beverage containersshould also possess good torque removal properties. Accordingly, inaddition to the above, a selected amount of a wax material can be addedto the plastic composition to improve torque removal. A microcrystallinewax has been found to work particularly well and is preferred. In fact,it has been discovered that addition of a small amount ofmicrocrystalline wax to the plastic composition described above improvesthe torque removal properties of the closure without significantlyaffecting the other desirable properties, such as oxygen barrierproperties of the composition. Microcrystalline waxes suitable forinclusion in the plastic composition of the present invention can be ahighly branched chain hydrocarbon of the aliphatic-alicyclic alkanefamily. Such waxes are sold under the name Okerin-6080H and areavailable from Honeywell of Morristown, N.J.

[0038] Other additives may also be included to improve theprocessability of the composition blend. In one embodiment, ananti-blocking talc can be added to the blend. More specifically, theanti-blocking talc can be combined with polyisobutylene to preventagglomeration of the polyisobutylene during processing.

[0039] The above described compounds can be combined in proportions sothat the plastic composition, when formed into a liner for the closure,provides excellent oxygen barrier properties, torque removal properties,adhesion to the polymeric shell and is easy to process. Accordingly, inone preferred embodiment, the plastic composition can include betweenapproximately 40-70 parts, by weight, of the thermoplastic elastomer,approximately 15-30 parts, by weight, of the polyisobutylene andapproximately 10-35 parts of polybutylene. Additionally, the plasticcomposition can include 2-10 parts, by weight, of a wax, preferably amicrocrystalline wax. The plastic composition can further include lessthan approximately 3 parts, by weight, of an anti-blocking talc.

[0040] The relative proportions described above provide a plasticcomposition that can be molded into an effective liner for a plasticclosure with the properties described above. While adjustments to theabove-described proportions are possible, it has been discovered thatamounts of the components significantly outside of the ranges describedabove can result in a liner with certain properties that are inferior tothe properties possessed by liners that include the components in theproportions described above. For example, if the amount of polybutyleneis significantly below the lower end of the preferred range, theresultant liners may not adhere as well to the inner surface of theclosure. If, on the other hand, the amount of polybutylene issignificantly greater from the upper limit of the preferred range, theresultant liner may be too hard and, thus, negatively affect sealabilityof the closure to the container.

[0041] Too much polyisobutylene can result in a blend that is too softand viscous and, as a result, is more difficult to process. A loweramount of polyisobutylene, on the other hand, will reduce the oxygenbarrier properties of the liner.

[0042] In accordance with the method for making the plastic composition,the above described compounds can be combined as follows. In oneembodiment, the selected amount of polyisobutylene is first mixed withan anti-blocking talc in a Banbury-type mixer for approximately 2-4minutes. The selected amounts of the thermoplastic elastomer,polybutylene, and microcrystalline are then added.

[0043] In another embodiment, the thermoplastic elastomer is processedand mixed in, for example, a twin-screw mixer to a temperature notexceeding 225° C. After mixing, the selected amount of polyisobutylenecan be compounded with the thermoplastic elastomer followed by additionof the polybutylene. Finally, the microcrystalline wax is added to theblend while continuing to mix the compounds.

[0044] Alternatively, the thermoplastic elastomer and the polybutylenecan be initially combined and mixed to a temperature not exceeding 225°C. This is followed by adding a selected amount of polyisobutylene andfinally the microcrystalline wax. A preferred mixing temperature forpreparing the plastic composition, as set forth above, is less than 225°C. and, preferably, approximately 180° C. It has been discovered that attemperatures approaching approximately 225° C., some breakdown ofmaterial is observed. The compounds described above can be blendedtogether in ways that are known to those of skill in the art.

[0045] After compounding, the plastic composition of the presentinvention can be formed into a liner and combined with the closure shellto provide a closure as shown in FIGS. 1-5. Liners of the presentinvention can be formed into discs or pads which can then be cold punchmolded onto the inner surface of the closure shell. Alternatively,liners in a gasket-type shape can be injection molded and placed ontothe inner surface of the closure shell.

[0046] Liners of the present invention which have been formed into discsor pads can have a thickness of approximately 0.005-0.1 inches. Moretypically, the thickness of such liner discs or pads can beapproximately 0.012 inches, except that, as seen in FIG. 2, thethickness of the liner can be greater near or along the annularperiphery of the liner where it contacts the end finish of thecontainer. For example, in one embodiment the thickness of the linernear or along the annular periphery can be approximately 0.01-0.05inches and, more preferably, approximately 0.030-0.035 inches. Suchadded thickness provides added barrier material where oxygen ingress ismost likely to occur, namely, between the closure skirt and thecontainer.

[0047] Liners of the present invention exhibit good to excellent oxygenbarrier properties and are particularly useful liners for food andbeverage containers. For example, using an oxygen permeability measuringapparatus, Model Ox-Tran Ten.Fifty, available from MOCON® ofMinneapolis, Minn., liners in accordance with the present invention havean oxygen ingress rate of less than approximately 14.0 cc/m²/day atnormal atmospheric conditions. Indeed, liners of the present inventiontypically limit the oxygen ingress rate to between approximately 4-8cc/m²/day at normal atmospheric conditions. (Briefly, equipment of thetype described above measures oxygen ingress by introducing nitrogen gasinto a vessel sealed with a liner sample (plaque) or a closure fittedwith a liner. The nitrogen gas picks up any oxygen present within thesealed vessel. The nitrogen gas exits the vessel through an outlet andthe level of captured oxygen is recorded as an electronic signal andreported as cubic centimeters (cc) of oxygen permeating across a squaremeter (m²) of a plaque or into a package (closure with liner) in a day.)

[0048] Further details regarding liners made from the compositions andthe advantages provided by the present invention will become apparentfrom the following illustrative working examples.

EXAMPLE 1

[0049] Samples of the plastic composition made in accordance with thepresent invention were prepared by blending approximately 65 parts of athermoplastic elastomer that includes a homopolymer or copolymer ofpolypropylene and a butyl-based rubber, 20 parts polyisobutylene, 15parts polybutylene and 4 parts microcrystalline wax. The composition wasformed into a liner and molded to the inner surface of a polypropyleneshell. Oxygen ingress through the closure with the liner was measuredusing the MOCON® permeation measuring equipment referred to above.Oxygen ingress into the container through a closure having a diameter ofapproximately 43 mm and including a liner made from the compositiondescribed above was measured as approximately 0.0024-0.005cc/pkg/day/atm.

[0050] Closures of different sizes (diameters) were also provided withliners made in accordance with the present invention on the one hand andliners made from a SEBS block copolymer, mineral oil and lubricant onthe other hand. As shown in Table 1, when compared to closures having aliner made from a SEBS block copolymer, mineral oil and lubricant(identified as 615), closures with liners made in accordance with thepresent invention (identified as 622) consistently displayed superioroxygen barrier properties (i.e., less oxygen ingress).

[0051] Also, as shown in Table I, oxygen ingress through a plasticbottle (i.e., either a mono-layered PET or multi-layered bottle) withclosures of different size having liners of different shapes was alsomeasured. Again, bottles fitted with closures that included liners madein accordance with the present invention (identified as 622)consistently exhibited lower oxygen ingress than bottles fitted withclosures having liners made from other plastic compositions. TABLE ICOMPARISON OF OXYGEN INGRESS THROUGH DIFFERENT LINERS MOCON OxygenIngress (ppm/1 Year) (cc/package/day/atm.) Mono-layer Size Closure LinerProfile Liner Material High Low Average PET*** Multi-layered**** 38 mmFlat 615 0.0150 35 13 38 mm Flat 622 0.0019 0.0011 0.0015 27 6 38 mmPlug 622 0.0069 0.0044 0.0058 30 8 38 mm Plug 615 0.0219 0.0180 0.019337 16 38 mm Plug 622 0.0111 0.0090 0.0104 32 12 38 mm Aseptic 615 0.015035 13 38 mm Aseptic 622 0.0036 0.0032 0.0035 28 7 43 mm Flat 615 0.02400.0160 0.018 36 15 43 mm Flat 622 0.0060 0.0018 0.003-0.005 28 7 63 mmFull Pad 615 0.0520 0.0350 0.036-0.042 46 25 63 mm Full Pad 622 0.01440.0107 0.0130 33 12 63 mm Ring Lined 615 0.0430 50 29 63 mm Ring Lined622 0.0160 0.0130 0.0140 34 13 82 mm** Ring Lined 615 0.0452 0.03920.0410 49 28 82 mm** Ring Lined 622 0.0401 0.0243 0.0319 44 22

EXAMPLE 2

[0052] Oxygen ingress through the liner alone (without the closure cap)was also measured. Sample plaques made from the plastic linercomposition of Example 1 and measuring approximately 4×4×0.060 incheswere prepared and were measured for oxygen ingress using MOCON®permeation measuring equipment. For comparison, sample plaques made fromonly the thermoplastic elastomer (without polyisobutylene, polybutyleneand microcrystalline wax) were prepared and also measured for oxygeningress. Oxygen ingress across the plaque made from the linercomposition of the present invention was approximately 4.8-7.9cc/m²/day/atm. By comparison, oxygen ingress across the plaque made fromthe thermoplastic elastomer alone was approximately 14.4 cc/m²/day.

[0053] In addition to the above, liners of the present invention exhibitexcellent adhesion to the polypropylene shells often used for beveragecontainers. Liners of the present invention made from the plasticcomposition also exhibit excellent mechanical and physical strength. Forexample, liners made from the preferred plastic compositions describedabove exhibit a 100% modulus of greater than approximately 260 psi. Apercent elongation of greater than approximately 350 and a tensilestrength of greater than approximately 500 psi.

EXAMPLE 3 Modulus, Elongation and Tensile Strength

[0054] Samples of the plastic composition were prepared by blendingapproximately 65 parts thermoplastic elastomer that includes ahomopolymer or copolymer of polypropylene and a butyl-based rubber, 20parts polyisobutylene, 15 parts polybutylene and 4 partsmicrocrystalline wax. The blend was extruded into a 0.060×6×6 (inch)plaque from which samples were die cut in accordance with ASTM D412procedures. The samples were tested for 100% modulus psi percentelongation and tensile strength psi (ASTM D412). Three lots of thecomposition made in accordance with the present invention were preparedand average values are set forth below in Table II. For comparison, alot of the thermoplastic elastomer alone (without the polybutylene,polyisobutylene and microcrystalline wax) was similarly tested for 100%modulus psi, elongation and tensile strength psi. The results of suchtesting are likewise reported in Table II under the heading “TPE.” Asseen from Table II, the plastic composition of the present invention(identified as 622) was also superior in these mechanical and physicalproperties. TABLE II 622 TPE 100% Modulus 337 255 Elongation % 460 332Tensile psi 667 481

[0055] The above described closures were also tested for adhesion to thepolypropylene shell. In general, liners made in accordance with thepresent invention exhibited excellent adhesion to the shell.

[0056] The present invention has been described in the context of itspreferred embodiments. It will be apparent to those skilled in the art,however, that modifications and variations therefrom can be made withoutdeparting from the spirit and scope of this invention. Accordingly, thisinvention is to be construed by the scope of the appended claims.

That which is claimed:
 1. A substantially oil-free closure cap liner orgasket composition comprising a blend of a thermoplastic elastomer,polybutylene and polyisobutylene.
 2. The composition of claim 1 furthercomprising a microcrystalline wax.
 3. The composition of claim 1 whereinsaid blend comprises, by weight, between approximately 40 to 70 partsthermoplastic elastomer, approximately 15 to 30 parts polyisobutyleneand approximately 10 to 35 parts polybutylene.
 4. The composition ofclaim 1 wherein said blend comprises, by weight, approximately 65 partsthermoplastic elastomer, approximately 20 parts polyisobutylene andapproximately 15 parts polybutylene.
 5. The composition of claim 2wherein said blend comprises, by weight, approximately 65 partsthermoplastic elastomer, approximately 20 parts polyisobutylene,approximately 15 parts polybutylene and approximately 4 partsmicrocrystalline wax.
 6. The composition of claim 1 wherein saidthermoplastic elastomer comprises a polyolefin, a butyl-based rubber anda lubricant.
 7. The composition of claim 1, wherein said compositionexhibits a 100% modulus of greater than approximately 280 psi, a percentelongation of greater than approximately 400 and a tensile strength ofgreater than approximately 500 psi.
 8. A closure comprising; a plasticshell having an end panel and an integral skirt downwardly extendingfrom the periphery thereof; said end panel having an inner surface; asubstantially oxygen impermeant liner adhered to at least a portion ofsaid inner surface, wherein said liner comprises a blend of athermoplastic elastomer, polybutylene and polyisobutylene.
 9. Theclosure of claim 8 wherein said thermoplastic elastomer comprises apolyolefin, a butyl-based rubber and a lubricant.
 10. The closure ofclaim 8 wherein said thermoplastic elastomer comprises a blockcopolymer.
 11. The closure of claim 8 wherein said blend comprises, byweight, approximately 40 to 70 parts thermoplastic elastomer,approximately 15 to 30 parts polyisobutylene and approximately 10 to 35parts polybutylene.
 12. The closure of claim 11 wherein said blendcomprises, by weight, approximately 65 parts thermoplastic elastomer,approximately 20 parts polyisobutylene and approximately 15 partspolybutylene.
 13. The closure of claim 8 wherein said blend furthercomprises a microcrystalline wax.
 14. The closure of claim 13 whereinsaid blend comprises, by weight, approximately 65 parts thermoplasticelastomer, approximately 20 parts polyisobutylene, approximately 15parts polybutylene and approximately 4 parts microcrystalline wax. 15.The closure of claim 8 wherein said liner comprises a flat disk disposedover substantially the entire inner surface of said end panel.
 16. Theclosure of claim 8 wherein said liner comprises an annular ring disposedover the peripheral portion of the inner surface of said end panel. 17.The closure of claim 15 wherein said liner comprises an interior portionand a peripheral portion, said peripheral portion having a thicknessgreater than said interior portion.
 18. The closure of claim 17 whereinsaid peripheral portion has a thickness of approximately 0.030-0.035inches.
 19. The closure of claim 17 wherein said interior portion has athickness of approximately 0.010-0.015 inches.
 20. The closure of claim8 wherein said liner exhibits an average oxygen ingress rate of lessthan 14.0 cc/m²/day.
 21. The container closure of claim 8 wherein saidliner exhibits an average oxygen ingress rate of approximately 4.0-8.0cc/m²/day.
 22. A method for providing a liner for a container closurecomprising: combining a thermoplastic elastomer with selected amounts ofpolyisobutylene and polybutylene; mixing said thermoplastic elastomerwith said polyisobutylene and said polybutylene to provide a blend; andforming said blend into a circular liner.
 23. The method of claim 22further comprising adding a microcrystalline wax prior to forming saidblend into said liner.
 24. The method of claim 22 comprising combiningsaid thermoplastic elastomer with said polybutylene prior to adding saidpolyisobutylene.
 25. The method of claim 22 comprising: providing athermoplastic elastomer; combining polyisobutylene with said elastomer;adding said polybutylene to said combination of elastomer andpolyisobutylene.
 26. The method of claim 22 wherein said combining andmixing are carried out at a temperature not exceeding 225° C.
 27. Themethod of claim 26 wherein said combining and mixing are carried out ata temperature of approximately 180° C.
 28. The method of claim 22comprising combining, by weight, approximately 40 to 70 partsthermoplastic elastomer with approximately 15 to 30 partspolyisobutylene and approximately 10 to 35 parts polybutylene.
 29. Themethod of claim 22 comprising adding approximately 4 parts of saidmicrocrystalline wax to said blend.
 30. The method of claim 29comprising combining, by weight, approximately 65 parts thermoplasticelastomer, approximately 20 parts polyisobutylene, approximately 15parts polybutylene and approximately 4 parts microcrystalline wax. 31.The method of claim 22 further comprising forming said blend into saidliner by injection molding or cold punch molding.
 32. The method ofclaim 22 comprising first combining polyisobutylene with ananti-blocking talc prior to adding said thermoplastic elastomer and saidpolybutylene.